Thanks for the report Mark! We are working to get the way QNH is now implemented reworked completely and make it separated and synced for the CFD. This means changes for the Single Pilot Operations as well and we'll make sure this gets addressed by then as well.
We still sometimes see this issue but cannot really pinpoint what's causing it. All we know it's a rare one-off issue. If reloading the flight doesn't help try reinstalling the bus again and make sure to restart your PC after and let me know if it still happens.